Figure 3.

Gsc is required for secondary neural induction and mesoderm patterning in Activin-treated animal cap explants. (A) Experimental design (n=15 or more per experimental set) (B, C) Untreated animal caps develop into atypical epidermis, whereas Activin treatment leads to elongation and brain formation, visualized by Otx2 at the anterior pole (arrows). In addition, Otx2 expression in anterior endoderm can be seen in one of the explants (arrowhead). (D, E) Gsc-depleted caps elongate after treatment with Activin, but lack Otx2 neural staining. (F, G) Chd-depleted caps treated with Activin are unable to elongate, confirming the requirement of Chd for dorsal mesoderm and neural induction by Activin (Oelgeschläger et al, 2003). Insets show whole sibling embryos. (H) Quantitative RT–PCRs showing genes affected by depletion of Gsc include markers of anterior CNS, organizer, somites, and ventral mesoderm. Note that Vent1 expression is increased more than 20-fold by Gsc knockdown.